Wiper seal assembly

ABSTRACT

A hydraulically-operated annular blowout preventer, for controlling a wellbore and comprising a wiper seal assembly, is described. The wiper seal assembly comprises a discrete wiper seal, for preventing debris and/or contaminants from the wellbore from entering the hydraulic fluid chamber of the blowout preventer, a discrete pressure seal, positioned below and abutting the wiper seal in the same seal groove, for isolating the hydraulic chamber, and a retainer member for preventing both radial and axial movement of the wiper seal.

FIELD OF THE INVENTION

The present invention relates to a wiper seal assembly for use inblowout preventers in the oil and gas industry.

BACKGROUND OF THE INVENTION

Annular or spherical blowout preventers (BOPs) are large, hydraulicallyoperated valves used in the oil and gas industry to control a wellboreat the ground level. Annular BOPs primarily function to seal or closethe wellbore, when actuated, to thereby prevent a blowout.

Structurally, annular BOPs comprise a body formed by mating upper andlower housings that enclose a deformable, resilient sealing means forsealing the wellbore. The body further encloses a hydraulically operatedpiston, which actuates the opening and closing of the resilient means.

Contamination of the BOP hydraulic fluid system, by fluid and/or debrisfrom the wellbore, needs to be prevented in order for the BOP tofunction properly. Various types of pressure seals are used to provide aphysical separation between the fluids in the hydraulic fluid chamberand the wellbore. The prior art pressure seals conventionally used inthis service, however, have not satisfactorily withstood the damage anddegradation that occurs over time as a result of contaminants in thewellbore fluid. In addition, such common pressure seals are of a sizeand shape that they can roll or twist due to increasing pressure,thereby releasing their sealed engagement and allowing leakage of fluid.Accordingly, frequent inspection, repair and replacement of the commonpressure seals is required in order to prevent the leakage of wellborefluid into the hydraulic fluid system of the BOP.

One attempt to solve this problem has been to utilize what is known as asingle, dual-functioning wiper seal, which serves to provide:

-   -   a) a pressure seal for preventing leakage of fluid from the        wellbore into the hydraulic fluid system of the BOP, and    -   b) a wiper seal for preventing dirt and debris from the fluid in        the wellbore from entering the hydraulic fluid system.

Dual-functioning seals, however, are not effective pressure seals andare still prone to degradation over time. Frequent repair and/orreplacement of dual-functioning wiper seals continues to pose a problemfor BOP manufacturers and operators in the oil and gas industry.

There is therefore a need for a wiper seal assembly that is designed toeffectively seal the interface between the hydraulic fluid system of aBOP and the fluid within the wellbore, while at the same time resistingdamage caused by wellbore fluid contaminants.

SUMMARY OF THE INVENTION

A hydraulically-operated annular blowout preventer, for controlling awellbore, comprising a wiper seal assembly is described. The blowoutpreventer comprises:

-   -   a U-shaped annular lower housing, having upstanding, spaced        apart, inner and outer walls;    -   a vertically movable piston; and    -   an adapter ring connected to the outer wall and extending toward        the inner wall of the lower housing;        wherein the housing and the adapter ring form an annular        hydraulic fluid chamber. The upper end of the inner wall and the        adapter ring are spaced apart such as to define an annular gap.        The lower end of the piston is positioned within the chamber and        its upper end extends upwardly through the gap, thereby        providing a physical separation between the hydraulic fluid        chamber and the wellbore.

The inner wall of the housing and the adapter ring each form an annularperipheral groove at the gap and each groove contains:

-   -   a discrete wiper seal, for preventing debris and/or contaminants        from the wellbore from entering the hydraulic fluid chamber,    -   a discrete pressure seal, positioned below and abutting the        wiper seal, for isolating the hydraulic chamber at the gap, and    -   a retainer member for preventing both radial and axial movement        of the wiper seal.

Various advantages and features of the present invention will becomereadily understood from the following detailed description taken inconnection with the appended claims and the attached drawings, butomitting the main sealing means.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an annular blowout preventer showingtwo wiper seal assemblies as defined herein.

FIG. 2 is an amplified view of the wiper seal assemblies as shown inFIG. 1.

FIG. 3 is a further amplified view of one wiper seal assembly as shownin FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A wiper seal assembly will now be described with reference to FIGS. 1 to3.

By way of background, a hydraulically operated blowout preventer (BOP),generally identified by 10, comprises a body 1, having an upper housing2 and a lower housing 3 with a bore 4 extending therethrough. The bore 4is an extension of, and communicates with, the wellbore of the well (notshown).

The lower housing 3 is annular and U-shaped, having a base wall 5 andinner and outer, radially spaced apart, upwardly projecting walls 6, 7.The walls 5, 6 and 7 cooperate to form an annular hydraulic fluidchamber 8. The inner wall 6 defines a section of the bore 4, which formspart of the wellbore.

An adapter ring 10 is connected with the upper end of the outer wall 7and projects inwardly to partly close the upper end of the hydraulicfluid chamber 8. The upper end of the inner wall 6 and the adapter ring10 define an annular gap 9 between them.

An annular piston 12 is slidably received by the chamber 8. The annularpiston 12 comprises a vertically extending wall 13, an outwardlyprojecting lip 14 at the lower end of the piston wall 13 and an inwardlyprojecting lip 15 at the upper end of the wall 13. The outwardlyprojecting lip 14 is slidably positioned within the chamber 8, thevertically wall 13 extends through the gap 9, and the inwardlyprojecting lip 15 corresponds with the bore 4.

The vertical wall 13 of the piston 12 forms a first sealable interface17 with the inner wall 6 of the lower housing 3, and a second sealableinterface 19 with the adapter ring 10. First and second interfaces 17,19seal the annular gap 9 and serve to isolate the fluid in the hydraulicfluid chamber 8 from the fluid and/or contaminants in the bore 4.

Having regard to FIG. 2, a wiper seal assembly, generally referred to as20, is provided at each of the first and second interfaces 17,19. Thewiper seal assembly 20 comprises a discrete wiper seal 22 and a discretepressure seal 24 positioned within an annular peripheral groove 26 andbelow the wiper seal 22, so that the wiper seal 22 shields and protectsthe pressure seal 24 from damage and degradation due to contaminants inthe bore 4.

The wiper seal 22 may be extruded nitrile rubber having a durometerhardness of at least 70 (Shore A scale). In one preferred embodiment,the durometer hardness or the wiper seal 22 is between 85-95 Shore A. Ina more preferred embodiment, the durometer hardness of the wiper seal is95 Shore A.

The pressure seal 24 of the assembly provides a seal to prevent fluidand/or smaller contaminants that were not retained by the wiper seal 22from leaking into the hydraulic fluid chamber 8. The pressure seal 24may comprise a Polypak™ seal (Parker Seals, Utah, U.S.A.). In oneembodiment, the pressure seal 24 may be a rectangular Polypak™ seal(Parker Seals, Utah, U.S.A.) thereby reducing the rolling or twisting ofthe seal within the groove 26.

Each wiper seal assembly 20 further comprises a retainer member 28,which is specifically configured to retain the wiper seal 22 and thepressure seal 24 in place in the groove 26. At the first interface 17,the retainer member 28 is formed by a lateral flange 30, that isintegral to and projects outwardly from the inner wall 6, toward theinner surface of the piston's 12 vertical wall 13. At the secondinterface 19, a lateral flange 30 is integral to and projects inwardlyfrom the adapter ring 10 toward the outer surface of the piston's 12vertical wall 13.

In one embodiment, each retainer member 28 further comprises adownwardly depending lug 31 which projects from the lateral flange 30,thereby forming a “hook-shaped” configuration (see FIG. 3). Eachretainer member 28 thus releasably receives the wiper seal 22 in a“snap-fit” engagement and reduces both axial and radial movement of thewiper seal 22. The retainer member 28 further retains the pressure seal24 within the annular peripheral groove 26 by providing the lug 31,which extends downwardly into the peripheral groove 26 such that thepressure seal 24 within the groove 26 is abutted by the wiper seal 22.

In use then, the wiper seal 22 is retained in a “shielding” position atthe first interface 17, by interference fit, between the retainer member28 of the inner wall 6, the inner surface of the piston's 12 verticalwall 13 and the pressure seal 24. At the second interface 19, the wiperseal 22 is retained in position, by interference fit, between theretainer member 28 of the adapter ring 10, the outer surface of thepiston's 12 vertical wall 13 and the pressure seal 24.

In conclusions, the interlocking of the wiper seal 22 and retainermember 28 configuration is used to effectively reduce both the axial andradial movement of the wiper seal 22 and to anchor the wiper seal 22 ina shielding relation to the pressure seal 24 within an annular BOP.

Although preferred embodiments have been shown and described, it will beappreciated by those skilled in the art that various changes andmodifications to the wiper seal assembly defined herein might be madewithout departing from the scope of the invention. The terms andexpressions used in the preceding specification have been used herein asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding equivalents offeatures shown and described or portions thereof, it being recognizedthat the scope of the invention is defined and limited only by theclaims that follow.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A hydraulically-operated annular blowout preventer comprising: aU-shaped annular lower housing having upstanding spaced apart inner andouter walls; a vertically actuated piston; and an adapter ring connectedto the outer wall and extending toward the inner wall; wherein the lowerhousing and the adapter ring form an annular hydraulic chamber; theupper end of the inner wall and the adapter ring being spaced apart todefine an annular gap; the lower end of the piston being positionedwithin the chamber and its upper end extending through the gap; theinner wall and the adapter ring each forming an annular peripheralgroove at the gap; each groove containing: a discrete wiper seal, adiscrete pressure seal, positioned below and abutting the wiper seal,for isolating the hydraulic chamber in its outer surface at the gap, anda retainer member for resisting both radial and axial movement of thewiper seal.
 2. The blowout preventer as set forth in claim 1 whereineach retainer member comprises a lateral flange for retaining the wiperseal.
 3. The blowout preventer as set forth in claim 2 wherein eachretainer member further comprises a downwardly depending lug that isintegral to the lateral flange, for retaining the wiper seal.
 4. Theblowout preventer as set forth in claim 1 wherein the wiper seal and thepressure seal are positioned within the groove by interference fit. 5.The blowout preventer as set forth in claim 1 wherein the wiper seal isextruded nitrile rubber.
 6. The blowout preventer as set forth in claim5 wherein the wiper seal comprises rubber having a Shore A durometerhardness of at least
 70. 7. The blowout preventer as set forth in claim6 wherein the wiper seal comprises rubber having a Shore A durometerhardness between 85 and
 95. 8. The blowout preventer as set forth inclaim 7 wherein the wiper seal comprises rubber having a Shore Adurometer hardness of
 90. 9. The blowout preventer in claim 1 whereinthe pressure seal is a rectangular Polypak™ pressure seal.